Tunable electronic properties of low-dimensional materials have been the object of extensive research, as such properties are highly desirable in order to provide flexibility in the design and optimization of functional devices. In this study, we account for the fact that such properties can be tuned by embedding diverse metal atoms and theoretically study a series of new organometallic porous sheets based on two-dimensional tetraoxa[8]circulene (TOC) polymers doped with alkali or alkaline-earth metals. The results reveal that the metal-decorated sheets change their electronic structure from semiconducting to metallic behaviour due to n-doping. Complete active space self-consistent field (CASSCF) calculations reveal a unique open-shell singlet ground state in the TOC–Ca complex, which is formed by two closed-shell species. Moreover, Ca becomes a doublet state, which is promising for magnetic quantum bit applications due to the long spin coherence time. Ca-doped TOC also demonstrates a high density of states in the vicinity of the Fermi level and induced superconductivity. Using the ab initio Eliashberg formalism, we find that the TOC–Ca polymers are phonon-mediated superconductors with a critical temperature T_C = 14.5 K, which is within the range of typical carbon based superconducting materials. Therefore, combining the proved superconductivity and the long spin lifetime in doublet Ca, such materials could be an ideal platform for the realization of quantum bits.

Conjugated polymers gain much attention due to the promising applications in organic electronic device technology. In this work, we theoretically study the structures and electronic properties of a novel class of nanostructures, namely one-dimensional tetrathia[8]circulenes (TTC) and tetraselena[8]circulenes (TSC) predicted to be promising semiconducting soft materials. It is found that all nanoribbons are thermodynamically stable and that their electronic properties depend significantly on the type of fusing between the monomers. In particular, the band gap tends to decrease while moving from the directly fused TTC/TSC ribbons to the structures coupled via a benzene-core linker and then to the ribbons fused through a four-membered ring. Therefore, both coupling type and length of oligomers allow one to manipulate the electronic and optical properties of the studied ribbons. The band structure calculations of infinite nanoribbons reveal direct band gaps that decrease from 2.28 to 2.14 eV for the TTC ribbons of the first and second fusion types. The TSC structures demonstrate the same trend exhibiting band gap narrowing from 2.41 (type I) up to 2.11 eV (type II). The type III ribbons possess a lack of periodicity due to the close-lying energy minima for the possible twisting configurations of TTC and TSC moieties relative to the linking four-membered ring.